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TextBoxBase.Clear Method

Clears all text from the text box control.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public void Clear()

You can use this method to clear the contents of the control instead of assigning the Text property an empty string.

The following code example uses TextBox, a derived class, to create an event handler for the TextChanged event. The code within the event handler restricts data to numbers. After text has been entered in the control, the code determines if the text entered is a number. If the text is not a number, the code clears the text from the control and a MessageBox is displayed to alert the user that only numbers are accepted. The example requires that a Boolean variable named flag and a TextBox control called textBox1 are defined outside of this method. This example demonstrates how to use a flag variable to avoid a cascading event in the TextChanged event.

private bool flag;

private void MyTextChangedHandler(System.Object sender, System.EventArgs e)
    long val;    
    // Check the flag to prevent code re-entry. 
    if(flag == false)
       // Set the flag to True to prevent re-entry of the code below.
       flag = true;
       // Determine if the text of the control is a number.
       try {
          // Attempt to convert to long
          val = System.Convert.ToInt64(textBox1.Text);
       catch {
          // Display a message box and clear the contents if not a number.
          MessageBox.Show("The text is not a valid number. Please re-enter");
          // Clear the contents of the text box to allow re-entry.
       // Reset the flag so other TextChanged events are processed correctly.
       flag = false;

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.